As a pendulum swings , its energy is constantly converted between kinetic energy and potential?

Energy is not a physical unit. It is a philosophical concept and an accounting technique used to analyze mechanical and chemical exchanges. In nuclear physics it is defined as a wavelength of light, in biology it is a synonym for metabolism, and in public utilities they say energy when they mean connectivity. Anybody who uses the word in any other context either does not know what he is talking about, or is peddling something you don't need.

Potential energy is defined as "the energy possessed by a body by virtue of its position relative to others, stresses within itself, electric charge, and other factors."

Kinetic energy is defined as "energy that a body possesses by virtue of being in motion."

In physics, energy is defined as "the property of matter and radiation that is manifest as a capacity to perform work (such as causing motion or the interaction of molecules)." But work is defined as disordering of energy, so that is a circular definition.

The definitions are not adequate to give any clear answer to the question. A pendulum works because of momentum, which is much clearer and easier to calculate.